The modernisation of the K2 fleet in Brno, the biggest customer of the type, included the complete re-modelling of the front end, and the upgrading of their electronic equipment.

These modernised examples were labeled K2R, whereby the 'R' stands for czech word rekonstrukce (in translate 'reconstructed').

Production of the type ended prematurely in 1970 as the vehicles were not well suited to the comparatively heavy traffic in Russian cities.

The only K2SU to remain in active service was in Yekaterinburg where it was retained as an historic vehicle until 1998.

One of the most noticeable differences were the corrugated sides and the pantograph, which was in the first series located at the rear of the tram, instead of the front (however it was eventually moved to the front in the 2000s for easier access).